Tape cassettes for use in magnetic recording and reproducing devices are typically of the type having a housing containing freely rotatably mounted reels on which is wound a magnetic tape. The tape extends between the reels and is guided across an access area, i.e., an access opening, in the housing. During use, as for example in a video recorder, the magnetic tape is withdrawn from the cassette housing out of the access area and wrapped or loaded about a guide drum. The guide drum is adjacent to a rotary magnetic head that scans tracks on the tape as the tape is moved about the guide drum. For effective use, the magnetic tape must be freely drawn out of the access area during the loading, recording, and reproducing modes; however, it must also be drawn out of the access area under controlled conditions such that it does not become excessively loose or slack.
Excessive looseness or slackness in the length of the magnetic tape extending between the reels can cause numerous problems. For example, if excessively loose or slack, magnetic tape typically does not become properly engaged by the magnetic head during use. This can lead to defective recording and/or reproducing operations. Furthermore, if excessively loose or slack, magnetic tape can jam within the cassette or within the recording and/or reproducing device, during use. Also, if excessively loose or slack, the extended run of magnetic tape can become damaged during storage or nonuse of the tape cassette.
Excessive looseness or slackness in the magnetic recording tape can arise when the cassette is being transported or is otherwise separated from its associated recording and/or reproducing device. Although some cassettes have locks that restrict rotation of the reels when the cassette is not in such device, it is possible that one or both of the reels within the cassette housing can turn to unwind the tape and develop the undesirable slack condition. Excessive slackness in the tape can also occur when the tape is engaged within a recording and/or reproducing device. Typically, such a device has spindles that engage the two reels. If driving and braking of the reels during operation by these spindles is not synchronous, slack in the tape can develop.
Elimination of excessive looseness or slackness in the magnetic tape as it is drawn out of the access area is typically accomplished using a slack limiting device, such as a slack limiting tab. Slack limiting tabs are designed to press against the moving tape at, or close to, guides located at opposite ends of the access opening within the cassette housing. Slack limiting tabs are designed to provide sufficient tension and exert a restraining or tightening effect on the tape without generating too much friction, which could cause, for example, excessive wear. In this way, slack limiting tabs preload the magnetic tape so it does not inadvertently unwind.
A slack limiting tab typically includes a resilient, flexible strip, usually of metal or plastic. Typically, one end of a slack limiting tab is affixed to the cassette housing, while the other end, i.e., the free end which exerts the tension against the tape, is typically coated with a layer of a low friction material. The most commonly used slack limiting tabs are made of polyester or polypropylene. However, some cassettes experience excessively loose or slack tape during use, despite the presence of a slack limiting tab. Therefore, there is a need for a magnetic tape cassette that functions properly, without excessive looseness or slackness, throughout the life of the cassette.